Boundary Layer Behaviour in Circular EHL Contacts in the Elastic-Piezoviscous Regime

Abstract

The solution of elastohydrodynamically lubricated contacts at high loads and/or low speeds can be described as a Hertzian pressure with inlet and outlet boundary layers: zones where significant pressure flow occurs. For the soft lubrication regime (elastic-isoviscous), a self-similar solution exists in the boundary layers satisfying localized equations. In this paper, the boundary layer behaviour in the elastic-piezoviscous regime is investigated. The lengthscale of the boundary layers and the scaling of pressure and film thickness are expressed in non-dimensional parameters. The boundary layer width scales as 1/M−−√ (equivalent to λ¯3/8 ), the maximum pressure difference relative to the Hertzian solution as 1/M−−√3 (equivalent to λ¯1/4 ) and the film thickness as 1/M−−√16 (equivalent to λ¯3/64 ) with M the Moes non-dimensional load and λ¯ a dimensionless speed parameter. The Moes dimensionless lubricant parameter L was fixed. These scalings differ from the isoviscous-elastic (soft lubrication) regime. With increasing load (decreasing speed), the solution exhibits an increasing degree of rotational symmetry. The pressure varies less than 10 % over an angle less than 45 degrees from the lubricant entrainment direction. The results provide additional fundamental understanding of the nature of elastohydrodynamic lubrication and give physical rationale to the finding of roughness deformation depending on the “inlet length”. The findings may contribute to more efficient numerical solutions and to improved semi-analytical prediction methods for engineering based on physically correct asymptotic behaviour.